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四川盆地聚(ju)居著四川省和(he)重(zhong)慶市大部分人(ren)口、居民主要(yao)為(wei)漢族巴(ba)蜀民系。是中(zhong)國和(he)世界上人(ren)口最多的區域(yu)之一(yi)。
中國(guo)著名紅(hong)層盆(pen)地，中國(guo)各大盆(pen)地中形(xing)態最(zui)(zui)典型、緯(wei)度最(zui)(zui)南、海(hai)(hai)拔最(zui)(zui)低的(de)盆(pen)地。位于長(chang)江上游地區，海(hai)(hai)拔500米左右，長(chang)江把它和(he)東海(hai)(hai)一(yi)脈相連，它是中國(guo)最(zui)(zui)大的(de)外流盆(pen)地。
四川(chuan)(chuan)(chuan)盆地(di)(di)(di)(di)(di)(di)的(de)面(mian)積(ji)約(yue)(yue)26萬(wan)余平(ping)方(fang)千米（面(mian)積(ji)是(shi)(shi)居(ju)第五第六位(wei)的(de)兩湖盆地(di)(di)(di)(di)(di)(di)和(he)銀額盆地(di)(di)(di)(di)(di)(di)的(de)兩倍），占(zhan)四川(chuan)(chuan)(chuan)省面(mian)積(ji)的(de)46%。四川(chuan)(chuan)(chuan)盆地(di)(di)(di)(di)(di)(di)西(xi)(xi)(xi)(xi)依(yi)青藏(zang)高(gao)原(yuan)和(he)橫斷山(shan)(shan)脈，北(bei)(bei)近秦巴(ba)山(shan)(shan)脈，與(yu)漢中(zhong)盆地(di)(di)(di)(di)(di)(di)相望，東接(jie)湘鄂西(xi)(xi)(xi)(xi)山(shan)(shan)地(di)(di)(di)(di)(di)(di)，南連云(yun)貴高(gao)原(yuan)，盆地(di)(di)(di)(di)(di)(di)北(bei)(bei)緣(yuan)(yuan)米倉(cang)山(shan)(shan)，南緣(yuan)(yuan)大婁山(shan)(shan)，東緣(yuan)(yuan)巫山(shan)(shan)，西(xi)(xi)(xi)(xi)緣(yuan)(yuan)邛崍山(shan)(shan)，西(xi)(xi)(xi)(xi)北(bei)(bei)邊(bian)緣(yuan)(yuan)龍(long)門山(shan)(shan)，東北(bei)(bei)邊(bian)緣(yuan)(yuan)大巴(ba)山(shan)(shan)，西(xi)(xi)(xi)(xi)南邊(bian)緣(yuan)(yuan)大涼山(shan)(shan)，東南邊(bian)緣(yuan)(yuan)相望于(yu)武陵(ling)山(shan)(shan)。這里的(de)巖(yan)石，主要由紫(zi)紅色砂(sha)巖(yan)和(he)頁巖(yan)組成(cheng)。這兩種巖(yan)石極易(yi)風化發育成(cheng)紫(zi)色土(tu)(tu)。紫(zi)色土(tu)(tu)含有豐(feng)富的(de)鈣、磷、鉀等(deng)營養(yang)元素，是(shi)(shi)南方(fang)最肥沃的(de)自然土(tu)(tu)壤。四川(chuan)(chuan)(chuan)盆地(di)(di)(di)(di)(di)(di)是(shi)(shi)全(quan)國紫(zi)色土(tu)(tu)分(fen)布最集中(zhong)的(de)地(di)(di)(di)(di)(di)(di)方(fang)，向(xiang)有“紫(zi)色盆地(di)(di)(di)(di)(di)(di)”的(de)美稱(cheng)。四川(chuan)(chuan)(chuan)盆地(di)(di)(di)(di)(di)(di)底部面(mian)積(ji)約(yue)(yue)16萬(wan)多平(ping)方(fang)千米，按其地(di)(di)(di)(di)(di)(di)理差(cha)異，自西(xi)(xi)(xi)(xi)向(xiang)東又可分(fen)為(wei)成(cheng)都平(ping)原(yuan)、川(chuan)(chuan)(chuan)中(zhong)丘陵(ling)和(he)川(chuan)(chuan)(chuan)東平(ping)行嶺谷三部分(fen)。成(cheng)都平(ping)原(yuan)西(xi)(xi)(xi)(xi)方(fang)是(shi)(shi)龍(long)門山(shan)(shan)脈，東方(fang)是(shi)(shi)龍(long)泉山(shan)(shan)脈。
四川盆地(di)(di)可明顯分為邊(bian)緣山地(di)(di)和(he)盆地(di)(di)底(di)部(bu)兩(liang)大部(bu)分，其(qi)面積分別約為10萬多和(he)16多萬平方公里(li)。邊(bian)緣山地(di)(di)多中(zhong)山和(he)低(di)山。
景(jing)觀(guan)各要(yao)素過(guo)渡(du)性明顯(xian)，如動植(zhi)(zhi)物(wu)(wu)組(zu)成上分(fen)別滲(shen)透了(le)華中(zhong)區、西南區、青藏高原區和(he)華北(bei)區的成分(fen)。邊(bian)緣(yuan)山(shan)地(di)(di)區從下而(er)上一般具(ju)有2～5個(ge)垂直(zhi)自然分(fen)帶(dai)(dai)。邊(bian)緣(yuan)山(shan)地(di)(di)是四(si)川(chuan)多(duo)種經濟林(lin)(lin)木和(he)用材林(lin)(lin)基地(di)(di)。農業上水(shui)土流失較為嚴重。盆地(di)(di)底部多(duo)丘(qiu)陵、低山(shan)和(he)平原。地(di)(di)表組(zu)成物(wu)(wu)質新而(er)單一，多(duo)砂泥巖與(yu)第四(si)紀沉積物(wu)(wu)。氣候上屬(shu)中(zhong)亞熱帶(dai)(dai)，熱量(liang)遠比邊(bian)緣(yuan)山(shan)地(di)(di)為高，但降(jiang)水(shui)量(liang)不(bu)及(ji)邊(bian)緣(yuan)山(shan)地(di)(di)。植(zhi)(zhi)被為人工的次生林(lin)(lin)木所(suo)代替，覆被率低，耕(geng)地(di)(di)連片，夏伏旱和(he)洪澇是這一地(di)(di)區最(zui)大災(zai)害。
盆(pen)地(di)(di)(di)(di)內(nei)部地(di)(di)(di)(di)形地(di)(di)(di)(di)貌顯示(shi)出(chu)明顯的三分特點，即盆(pen)西平原地(di)(di)(di)(di)貌、盆(pen)中丘陵地(di)(di)(di)(di)貌和盆(pen)東山地(di)(di)(di)(di)地(di)(di)(di)(di)貌，三者以龍(long)泉山和華(hua)鎣(ying)山為(wei)界。
四川盆(pen)地(di)其輪(lun)廓形態總體近(jin)似長方形，形似信(xin)(xin)(xin)封(feng)(feng)(feng)狀，右傾斜置在亞洲(zhou)大陸，因此被地(di)理學(xue)者稱之(zhi)為信(xin)(xin)(xin)封(feng)(feng)(feng)盆(pen)地(di)。信(xin)(xin)(xin)封(feng)(feng)(feng)盆(pen)地(di)東部頂(ding)點(dian)云陽（靠近(jin)萬州），南部頂(ding)點(dian)敘永(靠近(jin)遵義(yi))，西部頂(ding)點(dian)雅安，北(bei)部頂(ding)點(dian)廣元。信(xin)(xin)(xin)封(feng)(feng)(feng)盆(pen)地(di)幾何中(zhong)心城市遂寧（幾何中(zhong)心點(dian)大致在蓬溪南部地(di)區），中(zhong)北(bei)部（內頂(ding)角）中(zhong)心城市南充(chong)，中(zhong)南部內頂(ding)角安岳。
四川盆(pen)地西部(bu)的(de)成都和東南部(bu)的(de)重慶皆為(wei)國(guo)家(jia)中心城市。
四川盆地由盆周(zhou)山地和盆地底(di)部構(gou)成。
盆周東部為(wei)(wei)長江三峽，南部為(wei)(wei)云貴高原，西(xi)部為(wei)(wei)青(qing)藏(zang)高原，北部為(wei)(wei)大(da)巴山。
盆(pen)地底部(bu)(bu)主要分為川(chuan)(chuan)東平行嶺谷、川(chuan)(chuan)中丘(qiu)陵(ling)和(he)川(chuan)(chuan)西(xi)成都平原(yuan)三部(bu)(bu)分。龍泉(quan)山是成都平原(yuan)和(he)川(chuan)(chuan)中丘(qiu)陵(ling)的(de)界(jie)山，華鎣(ying)山是川(chuan)(chuan)中丘(qiu)陵(ling)和(he)川(chuan)(chuan)東平行嶺谷的(de)界(jie)山。
（1）在(zai)龍泉山(shan)和龍門山(shan)、邛(qiong)崍(lai)山(shan)之(zhi)間的(de)盆(pen)西(xi)平(ping)(ping)原(yuan)，系斷裂下(xia)陷由(you)岷江(jiang)(jiang)(jiang)水(shui)系的(de)河(he)流(liu)(liu)沖積而(er)成(cheng)，面積約(yue)8000平(ping)(ping)方千米，為我國(guo)西(xi)南最大的(de)平(ping)(ping)原(yuan)，因(yin)成(cheng)都位于(yu)平(ping)(ping)原(yuan)之(zhi)中， 故稱成(cheng)都平(ping)(ping)原(yuan)。成(cheng)都平(ping)(ping)原(yuan)海(hai)拔460米～750米，地勢由(you)西(xi)北向東南傾斜，地表平(ping)(ping)坦，相(xiang)對高差一(yi)般(ban)不超過(guo)30米～50米，它由(you)岷江(jiang)(jiang)(jiang)、沱江(jiang)(jiang)(jiang)、涪江(jiang)(jiang)(jiang)、青衣江(jiang)(jiang)(jiang)等八條河(he)流(liu)(liu)沖積聯綴而(er)成(cheng)，土壤肥(fei)沃，河(he)渠稠密(mi)，有(you)著名的(de)都江(jiang)(jiang)(jiang)堰自流(liu)(liu)灌溉，自古以來(lai)素有(you)“天府”之(zhi)稱。
（2）在(zai)龍泉山(shan)和(he)華鎣山(shan)之(zhi)間的(de)盆中(zhong)丘陵(ling)，地勢(shi)低(di)矮，海拔(ba)大多(duo)在(zai)300米～500米之(zhi)間，相對高(gao)差50米～150米，地勢(shi)由北向南傾斜，巖層近(jin)于(yu)水平，在(zai)流水的(de)長期侵(qin)蝕切(qie)割作用(yong)下，形成臺階(jie)狀(zhuang)的(de)方山(shan)丘陵(ling)，南部(bu)多(duo)淺(qian)丘，北部(bu)多(duo)深丘。丘陵(ling)地表軟硬(ying)相間的(de)紫(zi)紅色砂、頁巖極易風化(hua)為(wei)紫(zi)色土，富含磷鉀，自(zi)然肥(fei)力較(jiao)高(gao)，宜種(zhong)性廣，是四川(chuan)全省糧食、經(jing)濟作物主(zhu)產區。
（3）華鎣山(shan)(shan)以(yi)東為盆東平行嶺(ling)(ling)谷區(qu)，由(you)多(duo)條近東北西南(nan)走向(xiang)(xiang)的(de)(de)條狀(zhuang)背(bei)斜(xie)山(shan)(shan)地(di)(di)與向(xiang)(xiang)斜(xie)寬谷組成(cheng)(cheng)，山(shan)(shan)地(di)(di)陡(dou)而(er)窄，高(gao)(gao)700米(mi)-1000米(mi)，其(qi)中，華鎣山(shan)(shan)高(gao)(gao)1705米(mi)，為盆地(di)(di)底部(bu)最高(gao)(gao)峰(feng)。山(shan)(shan)地(di)(di)頂部(bu)的(de)(de)石(shi)灰巖被雨水溶蝕后，常成(cheng)(cheng)凹槽(cao)(cao)，故(gu)山(shan)(shan)地(di)(di)大多(duo)具(ju)有“一(yi)山(shan)(shan)二嶺(ling)(ling)一(yi)槽(cao)(cao)”或(huo)“一(yi)山(shan)(shan)三嶺(ling)(ling)二槽(cao)(cao)”的(de)(de)特色。山(shan)(shan)嶺(ling)(ling)間的(de)(de)谷地(di)(di)寬而(er)緩(huan)，海拔300米(mi)～500米(mi)，其(qi)間丘(qiu)陵、平壩交錯分布，是平行嶺(ling)(ling)谷區(qu)工農業生產主要地(di)(di)區(qu)。
四(si)川盆地邊緣山地區(qu)屬強(qiang)烈(lie)上升的褶(zhe)皺帶。
地(di)貌顯著特(te)征是，海(hai)拔較高(gao)，過渡性明顯，均為一(yi)系列中(zhong)山(shan)(shan)(shan)(shan)(shan)和低山(shan)(shan)(shan)(shan)(shan)所圍繞。盆地(di)北緣米(mi)倉(cang)山(shan)(shan)(shan)(shan)(shan)、大(da)巴山(shan)(shan)(shan)(shan)(shan)近東西走向，是秦巴山(shan)(shan)(shan)(shan)(shan)地(di)南翼(yi)部分(fen)，海(hai)拔一(yi)般在1500米(mi)～2200米(mi)之間(jian)，山(shan)(shan)(shan)(shan)(shan)勢雄(xiong)偉，山(shan)(shan)(shan)(shan)(shan)坡陡峭(qiao)，溝谷深(shen)切，相對高(gao)差可達(da)500米(mi)～1000米(mi)；南緣大(da)婁山(shan)(shan)(shan)(shan)(shan)屬氣勢磅礴的(de)云貴高(gao)原(yuan)之一(yi)部分(fen)；西緣有龍門山(shan)(shan)(shan)(shan)(shan)、邛崍山(shan)(shan)(shan)(shan)(shan)、峨眉山(shan)(shan)(shan)(shan)(shan)，山(shan)(shan)(shan)(shan)(shan)脊海(hai)拔都在1500米(mi)至～3000米(mi)以上(shang)，相對高(gao)差可達(da)1000米(mi)，屬中(zhong)國(guo)地(di)勢第一(yi)級(ji)階梯。峨眉山(shan)(shan)(shan)(shan)(shan)頂峰高(gao)3099米(mi)，與附近的(de)平原(yuan)相對高(gao)差達(da)2660米(mi)，山(shan)(shan)(shan)(shan)(shan)勢巍峨秀麗，為中(zhong)國(guo)四大(da)佛教名山(shan)(shan)(shan)(shan)(shan)之一(yi)。
四(si)周為海(hai)拔2000～3000米的山(shan)(shan)(shan)脈和(he)高(gao)原(yuan)所環(huan)繞，北面(mian)(mian)是(shi)(shi)大(da)巴山(shan)(shan)(shan)、米倉山(shan)(shan)(shan)、龍門山(shan)(shan)(shan)，西面(mian)(mian)是(shi)(shi)青藏高(gao)原(yuan)邊緣的邛崍山(shan)(shan)(shan)、大(da)涼山(shan)(shan)(shan)，南面(mian)(mian)是(shi)(shi)大(da)婁山(shan)(shan)(shan)，東面(mian)(mian)是(shi)(shi)巫山(shan)(shan)(shan)。
無論從構造(zao)還是(shi)人(ren)地(di)(di)(di)貌上看，四(si)川(chuan)盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)都是(shi)一個(ge)典型的(de)(de)盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)。它從震(zhen)旦紀(ji)以(yi)來(lai)就是(shi)地(di)(di)(di)殼比(bi)較穩定的(de)(de)大(da)型拗陷(xian)區。晚三(san)(san)迭(die)紀(ji)的(de)(de)印(yin)支(zhi)運(yun)(yun)動中(zhong)(zhong)成為(wei)一個(ge)內(nei)陸湖盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)，但范圍要比(bi)今日的(de)(de)四(si)川(chuan)大(da)得多(duo)，中(zhong)(zhong)生代堆積了(le)厚達(da)3000～4000米的(de)(de)紫紅色(se)(se)的(de)(de)砂巖(yan)和頁巖(yan)，因此人(ren)們又(you)稱(cheng)它為(wei)“紅色(se)(se)盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)”或“紫色(se)(se)盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)”。中(zhong)(zhong)生代末期的(de)(de)四(si)川(chuan)運(yun)(yun)動使(shi)盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)周圍褶(zhe)(zhe)皺成山(shan)(shan)，中(zhong)(zhong)間相(xiang)對下陷(xian)，輪廓基本形(xing)成，盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)內(nei)部(bu)(bu)地(di)(di)(di)層(ceng)也發(fa)生大(da)規模(mo)的(de)(de)變形(xing)。東(dong)部(bu)(bu)出現(xian)一組(zu)北東(dong)向(xiang)的(de)(de)褶(zhe)(zhe)皺，稱(cheng)盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)東(dong)褶(zhe)(zhe)皺帶；中(zhong)(zhong)部(bu)(bu)形(xing)成穹窿(long)構造(zao)，稱(cheng)盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)中(zhong)(zhong)穹窿(long)帶；西(xi)部(bu)(bu)表現(xian)成為(wei)盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)沉陷(xian)帶，為(wei)今天盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)的(de)(de)三(san)(san)個(ge)地(di)(di)(di)貌區奠定了(le)基礎。新生代的(de)(de)喜馬拉雅運(yun)(yun)動使(shi)周圍山(shan)(shan)地(di)(di)(di)再(zai)次上升，盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)再(zai)次相(xiang)對下陷(xian)， 成都一帶下陷(xian)更深。同時(shi)，長江切(qie)穿巫(wu)山(shan)(shan)，滾滾東(dong)流，完(wan)成了(le)統一的(de)(de)長江水系，使(shi)內(nei)流盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)轉變為(wei)外(wai)流盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)。四(si)川(chuan)盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)可明顯分(fen)為(wei)邊(bian)緣山(shan)(shan)地(di)(di)(di)和盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)底部(bu)(bu)兩大(da)部(bu)(bu)分(fen)，其面積分(fen)別約為(wei)10萬(wan)多(duo)和16萬(wan)多(duo)平(ping)(ping)方千米。 四(si)川(chuan)盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)是(shi)我國最大(da)的(de)(de)外(wai)流盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)，面積26萬(wan)多(duo)平(ping)(ping)方千米。四(si)川(chuan)盆(pen)(pen)(pen)(pen)(pen)(pen)(pen)地(di)(di)(di)內(nei)部(bu)(bu)丘陵、平(ping)(ping)原交錯，地(di)(di)(di)勢北高南低。由于地(di)(di)(di)表形(xing)態(tai)的(de)(de)不同，以(yi)華(hua)鎣山(shan)(shan)、龍泉山(shan)(shan)為(wei)界。
盆底可分(fen)為三(san)部分(fen)：
①華鎣(ying)山以(yi)東為大致平行的川東嶺谷，由(you)東北—西南走向(xiang)的許多條狀(zhuang)山體組成，海拔(ba)一般在700～800米(mi)，谷地中多低丘與平壩，海拔(ba)200～500米(mi)，是川東農業(ye)和人口集(ji)中的地方。
②華鎣山和龍泉(quan)山之(zhi)間為方(fang)山丘(qiu)陵，即川(chuan)中丘(qiu)陵。區內(nei)由(you)于紫(zi)紅(hong)色(se)砂頁巖傾角(jiao)平緩，受切割后(hou)形成大片方(fang)山式丘(qiu)陵。海拔350～450米(mi)，相對高度(du)幾十(shi)米(mi)。當地勞(lao)動人民(min)利用方(fang)山山丘(qiu)土層深厚的特(te)點，把(ba)梯田(tian)一直修到(dao)山頂。
③龍(long)泉山以(yi)西為平(ping)原。稱為川西平(ping)原或(huo)成都平(ping)原，面積6000多(duo)平(ping)方千(qian)米，是四川盆地(di)最大的(de)平(ping)原，也(ye)是西南(nan)地(di)區最大的(de)平(ping)原，海拔約600米。
四(si)(si)(si)川(chuan)(chuan)(chuan)盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)屬(shu)揚子準(zhun)地(di)(di)(di)(di)(di)(di)臺(tai)四(si)(si)(si)川(chuan)(chuan)(chuan)臺(tai)坳。古生(sheng)(sheng)代時(shi)相(xiang)對隆起(qi)，缺乏泥(ni)盆(pen)(pen)(pen)(pen)系(xi)(xi)和石(shi)(shi)(shi)(shi)炭系(xi)(xi)。印支運(yun)(yun)動轉換(huan)為(wei)(wei)(wei)大(da)(da)型拗(ao)陷，晚(wan)燕山(shan)(shan)(shan)(shan)運(yun)(yun)動，特(te)別是喜馬拉雅運(yun)(yun)動后發(fa)生(sheng)(sheng)褶皺隆起(qi)。盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)的(de)(de)格局(ju)主要(yao)受北(bei)東—南西向及北(bei)西向兩(liang)條構(gou)造(zao)線控制，構(gou)成(cheng)了(le)典型的(de)(de)菱(ling)(ling)形(xing)盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)，四(si)(si)(si)川(chuan)(chuan)(chuan)廣(guang)元、四(si)(si)(si)川(chuan)(chuan)(chuan)雅安、四(si)(si)(si)川(chuan)(chuan)(chuan)敘永(yong)為(wei)(wei)(wei)菱(ling)(ling)形(xing)的(de)(de)四(si)(si)(si)頂(ding)(ding)點(dian)，東西兩(liang)邊(bian)(bian)稍(shao)長，為(wei)(wei)(wei)380～430公里，南北(bei)兩(liang)邊(bian)(bian)略短，為(wei)(wei)(wei)310～330公里。以(yi)(yi)(yi)上菱(ling)(ling)形(xing)四(si)(si)(si)頂(ding)(ding)點(dian)的(de)(de)連線與(yu)盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)內(nei)(nei)(nei)650～750米(mi)(mi)的(de)(de)等高線大(da)(da)體(ti)相(xiang)當(dang)，盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)底部(bu)(bu)與(yu)邊(bian)(bian)緣(yuan)山(shan)(shan)(shan)(shan)地(di)(di)(di)(di)(di)(di)也以(yi)(yi)(yi)此為(wei)(wei)(wei)分(fen)界(jie)。四(si)(si)(si)川(chuan)(chuan)(chuan)盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)在距今1.4億年以(yi)(yi)(yi)前，還是內(nei)(nei)(nei)陸湖盆(pen)(pen)(pen)(pen)。至距今6.6千萬年時(shi)，盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)邊(bian)(bian)緣(yuan)山(shan)(shan)(shan)(shan)地(di)(di)(di)(di)(di)(di)迅速(su)隆升，長江中上游(you)水系(xi)(xi)開始溝通。盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)內(nei)(nei)(nei)湖水東瀉奠定了(le)現今之地(di)(di)(di)(di)(di)(di)貌形(xing)態。盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)邊(bian)(bian)緣(yuan)多低(di)(di)山(shan)(shan)(shan)(shan)和中山(shan)(shan)(shan)(shan)，山(shan)(shan)(shan)(shan)勢(shi)陡峻(jun)，發(fa)源(yuan)盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)邊(bian)(bian)緣(yuan)山(shan)(shan)(shan)(shan)地(di)(di)(di)(di)(di)(di)的(de)(de)河(he)(he)流大(da)(da)多為(wei)(wei)(wei)“V”型谷，嶺谷高差都逾500～1 000米(mi)(mi)， 地(di)(di)(di)(di)(di)(di)表(biao)崎嶇，故(gu)歷史上就有“蜀道難，難于(yu)上青(qing)天(tian)”之說。山(shan)(shan)(shan)(shan)脊海(hai)拔大(da)(da)多在2000～3000米(mi)(mi)，西北(bei)部(bu)(bu)與(yu)西部(bu)(bu)可(ke)超過(guo)3000～4000米(mi)(mi)，如龍門山(shan)(shan)(shan)(shan)4984米(mi)(mi)，峨眉山(shan)(shan)(shan)(shan)3099米(mi)(mi)，小相(xiang)嶺4 791米(mi)(mi)。地(di)(di)(di)(di)(di)(di)表(biao)廣(guang)泛出露古生(sheng)(sheng)代及其以(yi)(yi)(yi)前的(de)(de)石(shi)(shi)(shi)(shi)灰巖(yan)(yan)，其次為(wei)(wei)(wei)板巖(yan)(yan)、片巖(yan)(yan)、結晶(jing)灰巖(yan)(yan)、石(shi)(shi)(shi)(shi)英(ying)巖(yan)(yan)、砂(sha)(sha)泥(ni)巖(yan)(yan)和礫巖(yan)(yan)，局(ju)部(bu)(bu)有花(hua)崗(gang)巖(yan)(yan)和玄(xuan)武巖(yan)(yan)。石(shi)(shi)(shi)(shi)灰巖(yan)(yan)分(fen)布(bu)區可(ke)見(jian)石(shi)(shi)(shi)(shi)林、溶洞(dong)、暗河(he)(he)、槽谷等喀(ka)斯特(te)地(di)(di)(di)(di)(di)(di)貌，盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)南緣(yuan)興(xing)文(wen)縣素(su)(su)有“石(shi)(shi)(shi)(shi)林洞(dong)鄉”之稱（見(jian)興(xing)文(wen)石(shi)(shi)(shi)(shi)林）。巫(wu)山(shan)(shan)(shan)(shan)十二峰和金佛山(shan)(shan)(shan)(shan)等名(ming)山(shan)(shan)(shan)(shan)主要(yao)也由(you)石(shi)(shi)(shi)(shi)灰巖(yan)(yan)發(fa)育(yu)而成(cheng)。由(you)石(shi)(shi)(shi)(shi)灰巖(yan)(yan)、玄(xuan)武巖(yan)(yan)、花(hua)崗(gang)巖(yan)(yan)等組成(cheng)的(de)(de)峨眉山(shan)(shan)(shan)(shan)及由(you)砂(sha)(sha)泥(ni)巖(yan)(yan)、礫巖(yan)(yan)組成(cheng)的(de)(de)青(qing)城(cheng)山(shan)(shan)(shan)(shan)，素(su)(su)有“峨眉天(tian)下(xia)秀”、“青(qing)城(cheng)天(tian)下(xia)幽(you)”之稱，為(wei)(wei)(wei)中國(guo)著名(ming)游(you)覽勝地(di)(di)(di)(di)(di)(di)。盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)底部(bu)(bu)海(hai)拔多數在250～700米(mi)(mi)，地(di)(di)(di)(di)(di)(di)勢(shi)東南傾(qing)，盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)內(nei)(nei)(nei)各河(he)(he)流均(jun)由(you)邊(bian)(bian)緣(yuan)山(shan)(shan)(shan)(shan)地(di)(di)(di)(di)(di)(di)匯聚盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)底部(bu)(bu)的(de)(de)長江干流，形(xing)成(cheng)向心(xin)狀水系(xi)(xi)。地(di)(di)(di)(di)(di)(di)表(biao)為(wei)(wei)(wei)大(da)(da)面(mian)積的(de)(de)中生(sheng)(sheng)代紫紅色砂(sha)(sha)巖(yan)(yan)與(yu)泥(ni)巖(yan)(yan)所覆(fu)蓋，故(gu)稱為(wei)(wei)(wei)“紅層(ceng)盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)”，是中國(guo)中生(sheng)(sheng)代陸相(xiang)紅層(ceng)分(fen)布(bu)最(zui)集(ji)中地(di)(di)(di)(di)(di)(di)區。四(si)(si)(si)川(chuan)(chuan)(chuan)盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)為(wei)(wei)(wei)丘(qiu)陵(ling)(ling)性盆(pen)(pen)(pen)(pen)地(di)(di)(di)(di)(di)(di)，底部(bu)(bu)以(yi)(yi)(yi)丘(qiu)陵(ling)(ling)為(wei)(wei)(wei)主，次為(wei)(wei)(wei)低(di)(di)山(shan)(shan)(shan)(shan)和平原。
四川盆(pen)(pen)地(di)屬揚子陸臺一部分，稱(cheng)為四川陸臺，屬較穩(wen)定的(de)地(di)區(qu)，但仍經(jing)過(guo)兩次(ci)大(da)規模(mo)的(de)海(hai)浸。第一次(ci)從5億(yi)多年(nian)(nian)前(qian)的(de)寒武(wu)紀(ji)開始，延續到3.7億(yi)多年(nian)(nian)的(de)志留紀(ji)，不斷下陷成(cheng)了海(hai)洋盆(pen)(pen)地(di)，志留紀(ji)時發生加里東(dong)運(yun)動，除了西(xi)部的(de)龍門(men)山(shan)地(di)槽繼(ji)續下陷外，其余地(di)區(qu)上升為陸。2.7億(yi)年(nian)(nian)前(qian)的(de)石(shi)炭紀(ji)末，發生范(fan)圍更(geng)大(da)的(de)第二(er)次(ci)海(hai)浸，盆(pen)(pen)地(di)再次(ci)為海(hai)洋占據。二(er)疊紀(ji)時海(hai)陸交替，形成(cheng)重(zhong)慶附近的(de)南酮(tong)、松藻、天府(fu)等煤(mei)礦。二(er)疊紀(ji)末，盆(pen)(pen)地(di)西(xi)部巖漿噴出，峨(e)眉山(shan)小金頂及清音閣一帶(dai)的(de)玄武(wu)巖就在這時生成(cheng)。
距今1.9億(yi)年(nian)(nian)的(de)(de)(de)(de)三(san)疊(die)紀，“印支運動(dong)”使(shi)盆地(di)(di)邊緣逐漸隆起(qi)成(cheng)(cheng)山(shan)，被海(hai)水(shui)淹沒的(de)(de)(de)(de)地(di)(di)區(qu)逐漸上升(sheng)成(cheng)(cheng)陸，由(you)海(hai)盆轉為湖盆。當時(shi)(shi)湖水(shui)幾乎占據(ju)現(xian)今四(si)川盆地(di)(di)的(de)(de)(de)(de)全(quan)境(jing)，稱為“蜀湖”，從(cong)此結(jie)束了海(hai)浸(jin)的(de)(de)(de)(de)歷史。在(zai)中生(sheng)代漫長的(de)(de)(de)(de)1億(yi)多年(nian)(nian)里，盆地(di)(di)氣候溫(wen)暖濕潤，到(dao)處生(sheng)長蕨類、蘇(su)鐵和(he)裸(luo)子植物(wu)，是又一個成(cheng)(cheng)煤(mei)期，永榮煤(mei)礦即(ji)在(zai)三(san)疊(die)紀和(he)侏羅紀時(shi)(shi)形(xing)成(cheng)(cheng)。東起(qi)長壽、墊江(jiang)，西到(dao)江(jiang)油、邛崍，北抵大巴(ba)山(shan)麓，南到(dao)貴州赤水(shui)，還(huan)是天然氣富集區(qu)。這一時(shi)(shi)期爬行(xing)動(dong)物(wu)恐龍(long)(long)稱霸(ba)一時(shi)(shi)。1957年(nian)(nian)在(zai)合(he)州發(fa)現(xian)的(de)(de)(de)(de)“合(he)州馬門溪(xi)龍(long)(long)”身長22米，高(gao)3.5米，是中國(guo)亞洲(zhou)最(zui)大和(he)最(zui)完整的(de)(de)(de)(de)恐龍(long)(long)化石。
7000萬(wan)年(nian)前(qian)的(de)(de)(de)(de)(de)(de)白(bai)堊紀末期，發生(sheng)(sheng)又一次強烈的(de)(de)(de)(de)(de)(de)地(di)(di)(di)(di)(di)殼運動(dong)“燕山(shan)(shan)(shan)運動(dong)”。盆(pen)地(di)(di)(di)(di)(di)四周山(shan)(shan)(shan)地(di)(di)(di)(di)(di)繼(ji)續隆起，同時產生(sheng)(sheng)不少大(da)斷(duan)層(ceng)，如西部(bu)(bu)的(de)(de)(de)(de)(de)(de)龍(long)門山(shan)(shan)(shan)大(da)斷(duan)層(ceng)和(he)東部(bu)(bu)的(de)(de)(de)(de)(de)(de)華瑩(ying)山(shan)(shan)(shan)大(da)斷(duan)層(ceng)，把盆(pen)地(di)(di)(di)(di)(di)分為(wei)三(san)部(bu)(bu)分。蜀湖(hu)(hu)(hu)縮(suo)(suo)小為(wei)僅有2萬(wan)平方公(gong)里的(de)(de)(de)(de)(de)(de)蜀湖(hu)(hu)(hu)。封(feng)閉的(de)(de)(de)(de)(de)(de)盆(pen)地(di)(di)(di)(di)(di)地(di)(di)(di)(di)(di)形(xing)及急劇縮(suo)(suo)小的(de)(de)(de)(de)(de)(de)水面，使氣候逐漸變(bian)得(de)干熱，沉積(ji)(ji)物由(you)海相(xiang)、海陸(lu)交替相(xiang)變(bian)為(wei)陸(lu)相(xiang)，大(da)量風化、侵(qin)蝕(shi)、剝蝕(shi)的(de)(de)(de)(de)(de)(de)物質在盆(pen)地(di)(di)(di)(di)(di)堆積(ji)(ji)了數千(qian)米厚，形(xing)成(cheng)紅(hong)色(se)和(he)紫紅(hong)色(se)的(de)(de)(de)(de)(de)(de)砂、泥、頁巖。裸子植物不斷(duan)衰退，恐龍(long)滅(mie)絕(jue)了。內陸(lu)湖(hu)(hu)(hu)泊在干燥條件下，經(jing)強烈蒸發，濃度增大(da)，鹽分不斷(duan)積(ji)(ji)累(lei)，形(xing)成(cheng)鹽湖(hu)(hu)(hu)，后來泥沙掩埋(mai)而保(bao)存于地(di)(di)(di)(di)(di)層(ceng)之中(zhong)，經(jing)過漫長(chang)的(de)(de)(de)(de)(de)(de)地(di)(di)(di)(di)(di)質作(zuo)用形(xing)成(cheng)巖層(ceng)，自(zi)貢一帶是著名的(de)(de)(de)(de)(de)(de)井(jing)鹽產地(di)(di)(di)(di)(di)。 2000多萬(wan)年(nian)前(qian)的(de)(de)(de)(de)(de)(de)新第(di)(di)三(san)紀，受喜馬拉雅造(zao)山(shan)(shan)(shan)運動(dong)的(de)(de)(de)(de)(de)(de)影(ying)響。距今二、三(san)百(bai)萬(wan)年(nian)的(de)(de)(de)(de)(de)(de)第(di)(di)四紀，地(di)(di)(di)(di)(di)殼再次發生(sheng)(sheng)構(gou)造(zao)運動(dong)。從而，四川(chuan)盆(pen)地(di)(di)(di)(di)(di)由(you)內流盆(pen)地(di)(di)(di)(di)(di)變(bian)為(wei)外流陸(lu)盆(pen)，由(you)封(feng)閉的(de)(de)(de)(de)(de)(de)內流區(qu)(qu)變(bian)為(wei)外流區(qu)(qu)，由(you)以堆積(ji)(ji)為(wei)主變(bian)為(wei)侵(qin)蝕(shi)為(wei)主，經(jing)歷(li)了海盆(pen)——湖(hu)(hu)(hu)盆(pen)——陸(lu)盆(pen)的(de)(de)(de)(de)(de)(de)滄桑(sang)之變(bian)。 第(di)(di)四紀是冰川(chuan)廣布的(de)(de)(de)(de)(de)(de)時代，盆(pen)地(di)(di)(di)(di)(di)西北(bei)山(shan)(shan)(shan)地(di)(di)(di)(di)(di)發育大(da)量冰川(chuan)。冰川(chuan)消融后，大(da)量沉積(ji)(ji)物由(you)岷(min)江、沱江等(deng)攜帶，堆積(ji)(ji)在西部(bu)(bu)的(de)(de)(de)(de)(de)(de)凹(ao)陷區(qu)(qu)，即以前(qian)的(de)(de)(de)(de)(de)(de)蜀湖(hu)(hu)(hu)之中(zhong)，最終形(xing)成(cheng)了成(cheng)都(dou)平原。 四川(chuan)盆(pen)地(di)(di)(di)(di)(di)地(di)(di)(di)(di)(di)貌豐(feng)富(fu)，平原7%，丘陵52%，低山(shan)(shan)(shan)41%。
四(si)川(chuan)盆(pen)地(di)中植(zhi)物近萬種(zhong)(zhong)，古老而特有(you)(you)(you)(you)種(zhong)(zhong)之多為(wei)中國其他(ta)地(di)區所不及。在盆(pen)地(di)邊(bian)緣山(shan)(shan)地(di)及盆(pen)東平行(xing)嶺谷(gu)尚可見水杉(shan)、銀杉(shan)、鵝掌楸、檫木(mu)、三尖杉(shan)、珙桐(tong)、水青(qing)樹(shu)、連香樹(shu)、領春木(mu)、金錢槭(qi)、蠟梅、杜仲、紅(hong)豆杉(shan)、鐘萼木(mu)、福建(jian)柏、穗(sui)花杉(shan)、崖柏、木(mu)瓜紅(hong)等珍稀孑(jie)遺植(zhi)物與(yu)特有(you)(you)(you)(you)種(zhong)(zhong)。在濕(shi)熱河(he)谷(gu)可見桫(suo)(suo)欏、小羽桫(suo)(suo)欏、烏毛(mao)蕨(jue)、華(hua)南紫(zi)萁、里(li)白等古熱帶(dai)孑(jie)遺植(zhi)物。 四(si)川(chuan)盆(pen)地(di)的地(di)帶(dai)性植(zhi)被(bei)是亞熱帶(dai)常綠闊(kuo)(kuo)(kuo)葉林，其代表樹(shu)種(zhong)(zhong)有(you)(you)(you)(you)栲樹(shu)、峨眉栲、刺果(guo)米櫧(zhu)、青(qing)岡(gang)、曼青(qing)岡(gang)、包(bao)石櫟、華(hua)木(mu)荷(he)、大(da)包(bao)木(mu)荷(he)、四(si)川(chuan)大(da)頭茶、楨楠、潤楠等，海(hai)拔一般情況下在1600～1 800米以下。其次有(you)(you)(you)(you)馬尾松、杉(shan)木(mu)、柏木(mu)組(zu)成 的亞熱帶(dai)針葉林及竹林。 邊(bian)緣山(shan)(shan)地(di)從(cong)下而上是常綠闊(kuo)(kuo)(kuo)葉林、常綠闊(kuo)(kuo)(kuo)葉與(yu)落葉闊(kuo)(kuo)(kuo)葉混交林，寒(han)溫帶(dai)山(shan)(shan)地(di)針葉林，局部有(you)(you)(you)(you)亞高(gao)山(shan)(shan)灌(guan)叢草甸。
四川(chuan)盆(pen)地(di)(di)是中(zhong)國(guo)(guo)動物(wu)種(zhong)類最多、最齊全的(de)地(di)(di)區(qu)(qu)之(zhi)一(yi)。據(ju)統計，除魚(yu)類外(wai)，盆(pen)地(di)(di)底部共(gong)有(you)動物(wu)417種(zhong)，盆(pen)地(di)(di)西緣、北緣和南緣山(shan)(shan)地(di)(di)分別為(wei)487種(zhong)、317種(zhong)與288種(zhong)，其中(zhong)經濟(ji)動物(wu)均(jun)占一(yi)半(ban)以上。盆(pen)地(di)(di)西緣山(shan)(shan)地(di)(di)是中(zhong)國(guo)(guo)特(te)有(you)而古老(lao)動物(wu)保(bao)存最好(hao)、最集(ji)中(zhong)的(de)地(di)(di)區(qu)(qu)，屬于一(yi)類保(bao)護(hu)動物(wu)的(de)有(you)大熊貓(mao)(mao)、金(jin)(jin)絲猴、扭角(jiao)羚(ling)、灰金(jin)(jin)絲猴、白(bai)(bai)唇鹿(lu)等。還有(you)珍(zhen)貴特(te)有(you)動物(wu)小熊貓(mao)(mao)、雪豹(bao)、鬣羚(ling)、短尾(wei)猴、獼(mi)猴、毛冠鹿(lu)、水獺(ta)及鴛鴦、血(xue)雉、紅(hong)腹(fu)角(jiao)雉、綠(lv)尾(wei)虹雉、白(bai)(bai)腹(fu)錦(jin)雞、紅(hong)腹(fu)錦(jin)雞等。 盆(pen)地(di)(di)西緣的(de)平(ping)武、青川(chuan)、北川(chuan)、寶興(xing)、天全、洪雅、馬邊(bian)等地(di)(di)，均(jun)為(wei)中(zhong)國(guo)(guo)大熊貓(mao)(mao)的(de)主要(yao)分布區(qu)(qu)。已設立唐家河、王朗、臥龍(long)（見臥龍(long)自(zi)然(ran)保(bao)護(hu)區(qu)(qu)）、蜂(feng)桶寨、喇叭河等7處(chu)大熊貓(mao)(mao)、金(jin)(jin)絲猴等自(zi)然(ran)保(bao)護(hu)區(qu)(qu)。 酉(you)陽(yang)、馬邊(bian)、平(ping)武等盆(pen)地(di)(di)邊(bian)緣山(shan)(shan)地(di)(di)溪溝中(zhong)的(de)大鯢及長(chang)江、金(jin)(jin)沙江中(zhong)的(de)中(zhong)華鱘、白(bai)(bai)鱘也為(wei)四川(chuan)所特(te)有(you)，均(jun)屬國(guo)(guo)家保(bao)護(hu)動物(wu)。
四川盆地(di)有煤(mei)、鐵、天(tian)然氣、石(shi)油、鹽、芒(mang)硝、石(shi)膏、磷、硫、鋁、金、銅、錳、石(shi)墨、汞等(deng)礦(kuang)(kuang)產資源(yuan)，其中天(tian)然氣、芒(mang)硝為(wei)全中國之冠(guan)，并有中國重要的鍶礦(kuang)(kuang)。川東北是世界(jie)最大的天(tian)然氣富集區之一，川中和南充等(deng)地(di)鹽巖(yan)礦(kuang)(kuang)儲量很大。
四川盆(pen)地地形閉塞，由于(yu)北(bei)部(bu)(bu)秦嶺阻擋冷空(kong)氣，冬季氣溫(wen)高(gao)于(yu)同(tong)緯(wei)度其他地區。最(zui)冷月(yue)北(bei)部(bu)(bu)均(jun)溫(wen)3～5℃，南(nan)部(bu)(bu)5~8℃，較同(tong)緯(wei)度的上海、湖北(bei)、安徽及(ji)緯(wei)度偏南(nan)的貴(gui)州(zhou)高(gao)1～4℃。盆(pen)地北(bei)部(bu)(bu)極端(duan)最(zui)低(di)(di)溫(wen)-8～-5℃，南(nan)部(bu)(bu)-5℃~-2℃。霜(shuang)(shuang)雪(xue)少見，年(nian)無霜(shuang)(shuang)期長(chang)280～350天，同(tong)緯(wei)度上的武漢冬天卻霜(shuang)(shuang)雪(xue)不(bu)斷，盆(pen)地位于(yu)長(chang)江河谷中的長(chang)寧全年(nian)無霜(shuang)(shuang)。 盆(pen)地各地夏季始于(yu)5月(yue)底，終于(yu)9月(yue)中旬，夏長(chang)4個月(yue)，溫(wen)度上東高(gao)西(xi)低(di)(di)。盆(pen)地西(xi)部(bu)(bu)夏天平均(jun)氣溫(wen)約25℃，較同(tong)緯(wei)度的上海、武漢等城(cheng)市(shi)偏低(di)(di)3-4度，但濕度較大，所以悶(men)熱難忍。
東(dong)(dong)部最(zui)熱月(yue)氣(qi)溫(wen)高(gao)達26～29℃，長江(jiang)河谷(gu)局(ju)地(di)達到30℃。盛夏(xia)連晴高(gao)溫(wen)天氣(qi)又造(zao)成盆(pen)地(di)東(dong)(dong)南部嚴重(zhong)的(de)夏(xia)伏旱。盆(pen)地(di)氣(qi)溫(wen)東(dong)(dong)南高(gao)西(xi)北低(di)(di)(di)(di)，盆(pen)底高(gao)邊緣(yuan)(yuan)(yuan)低(di)(di)(di)(di)； 各(ge)地(di)年均溫(wen)16～18℃。10℃以上活(huo)動(dong)積溫(wen)4500～6000℃，持續期(qi)8～9個月(yue)，屬(shu)中亞(ya)熱帶(dai)(dai)。東(dong)(dong)南部的(de)長江(jiang)河谷(gu)積溫(wen)超過6000℃，相當于中國南嶺以南的(de)南亞(ya)熱帶(dai)(dai)氣(qi)候。盆(pen)地(di)氣(qi)溫(wen)東(dong)(dong)高(gao)西(xi)低(di)(di)(di)(di)，南高(gao)北低(di)(di)(di)(di)，盆(pen)底高(gao)而(er)邊緣(yuan)(yuan)(yuan)低(di)(di)(di)(di)，等(deng)溫(wen)線分布呈現同心圓狀。盆(pen)地(di)邊緣(yuan)(yuan)(yuan)山(shan)(shan)地(di)氣(qi)溫(wen)具有垂直分布特點，如峨眉山(shan)(shan)、金佛(fo)山(shan)(shan)海拔升高(gao)百(bai)米，氣(qi)溫(wen)遞減0.55℃和(he)0.61℃。峨眉山(shan)(shan)頂年均溫(wen)僅3℃，10℃以上活(huo)動(dong)積溫(wen)586℃，氣(qi)候上相當于寒溫(wen)帶(dai)(dai)和(he)亞(ya)寒帶(dai)(dai)。
四川盆(pen)地(di)(di)年(nian)降(jiang)水量1000～1300毫(hao)米，盆(pen)地(di)(di)邊緣山地(di)(di)降(jiang)水十分充沛，如樂山和雅(ya)安(an)間(jian)的(de)西緣山地(di)(di)年(nian)降(jiang)水量為(wei)1 500～1800毫(hao)米，為(wei)中(zhong)國(guo)突出的(de)多雨(yu)區(qu)，有“華(hua)西雨(yu)屏”之(zhi)稱。但(dan)冬(dong)干、春(chun)旱、夏澇、秋(qiu)綿雨(yu)，年(nian)內分配(pei)不均，70～75%的(de)雨(yu)量集中(zhong)于6～10月。最(zui)大日(ri)降(jiang)水量可達(da)300～500毫(hao)米。“巴(ba)山夜雨(yu)”自古聞名，夜雨(yu)占總雨(yu)量的(de)60～70%以上。盆(pen)地(di)(di)區(qu)霧大濕重，云(yun)低陰天多。峨眉山、金佛山是中(zhong)國(guo)霧日(ri)最(zui)多地(di)(di)區(qu)之(zhi)一，年(nian)相對濕度(du)之(zhi)高也為(wei)中(zhong)國(guo)之(zhi)冠。盆(pen)地(di)(di)年(nian)日(ri)照僅(jin)900～1300小時，年(nian)太陽輻射量為(wei)370～420千焦耳/平(ping)方厘米，均為(wei)中(zhong)國(guo)最(zui)低值，故有“蜀犬吠日(ri)”之(zhi)說。
